Образование в контексте идентификационных процессов (Субъект образования как следствие концептуальной рамки)

The available models for the prediction of fatigue crack growth in adhesive bonds rely on the similitude principle. In most cases, one of three similitude parameters based on the strain energy release rate (SERR) is used; i.e. Gmax, (Δ√G)2, or ΔG. In all cases it is usually observed that keeping the similitude parameter constant, and changing the R-ratio, results in a different crack growth rate. In this paper it is shown that this apparent ‘R-ratio’ effect is caused because the selected similitude parameter does not define a unique load cycle; a single value of the similitude parameter could correspond to infinitely many load cycles. The strain energy dissipation approach is used to show that the resistance to fatigue crack growth is related to the maximum applied load. The amount of energy available for crack growth is shown to be related to the applied cyclic work. With these relationships the R-ratio effects reported in literature can be qualitatively explained, purely in terms of the actual applied load cycle. Although it is possible that the material behaviour also depends on the R-ratio, the magnitude of these effects can only properly be determined if the applied load cycle is correctly described first.Structural Integrity & CompositesAerospace Structures & Material

Solid State Amorphisation - Thermodynamics and Kinetics

Mechanical Maritime and Materials Engineerin

Understanding the Fatigue Behavior of FML Structures and Materials under Complex Variable Amplitude Loading

This paper presents various failure mechanisms in FMLs, highlights the presence or absence of interaction effects, and describes how the failure mechanisms can be described for predicting damage growth under arbitrary complex load spectra.Aerospace Engineerin

Epoxy-resin adhesive and method for bonding using such an epoxy resin adhesive

The invention relates to an epoxy resin adhesive comprising a dotation of nano-substances, wherein the nano- substances are selected from the group comprising carbon-fibre nanotubes, carbon nano-fibres, silicate nano powders, and wherein the nano-substances are dispersed in the adhesive with a weight ratio of at least 1% and wherein the nano-substances are carbon-fibre nanotubes having a weight ratio of approximately 2%.Aerospace Engineerin

A large displacement orthotropic viscoelastic model for manufacturing-induced distortions in Fibre Metal Laminates

Distortions and residual stresses are predicted in Fibre Metal Laminates (FMLs) under large deformations. A new modelling procedure is presented for small and large deformation analysis of thermo-viscoelastic problems of orthotropic materials. The material model is implemented in a finite element package which can be used for cure and/or temperature dependent response of composites undergoing large rotations but with small strains.Temperature-dependent and viscoelastic responses are characterised for GLARE, as the mostly used type of FMLs. The geometrically nonlinear thermo-viscoelastic model is used to predict the manufacturing-induced warpage of panels. The curing stresses are calculated from a previously developed model accounting for chemical shrinkage and stiffness evolution of the prepreg layers during cure. The shape deviation of some non-symmetric GLARE panels are predicted and compared to the real measurement of fabricated laminates. The accuracy of the model is verified which can be used in further studies to improve the precision of manufacturing and assembly and also to have better prediction of the fatigue life and residual strength.Structural Integrity & CompositesAerospace Structures & Material

Optimization of light scattering enhancement by gold nanoparticles in fused silica optical fiber

A conventional distributed fiber optic sensing system offers close to linear sensitivity along the fiber length. However gold nanoparticles (NP) have been shown to be able to enhance the contrast ratio to improve the quality of signal detection. The challenge in improving the contrast of reflected signals is to optimise the nanoparticle doping concentration over the densed sensing length to make best use of the distributed fiber sensing hardware. In this paper, light enhancement by spherical gold NPs in the optical fibers was analyzed by considering the size-induced NP refractive index changes. This was achieved by building a new model to relate backscattered light from a gold NP suspension between the optical fiber end tips and backscattered light from gold NPs in the core of the optical fiber. The paper provides a model to determine the optimized sizes and concentrations of NPs for sensing at different desired penetration depths in the optical fiber.Structural Integrity & Composite

Extreme prognostics for remaining useful life analysis of composite structures

The procedure of fatigue damage accumulation in composite structures is still unknown and depends on several parameters such as type and frequency of loading, stacking sequence and material properties. Additionally, the nonhomogeneous and anisotropic nature of composites result to a stochastic activation of the different failure mechanisms and make the estimation of remaining useful life (RUL) very complex but interesting task. Data driven probabilistic methodologies have found increasing use the last decade and provide a platform for reliable estimations of RUL utilizing condition monitoring (CM) data. However, the fatigue life of a specific composite structure has a quite significant scatter, with specimens that either underperform or outperform. These specimens are often referred as outliers and the estimation of their RUL is challenging. This study proposes a new RUL probabilistic model, the Extreme Non-Homogenous Hidden Semi Markov Model (ENHHSMM) which is an extension of the Non-Homogenous Hidden Semi Markov Model (NHHSMM). The ENHHSMM uses dynamic diagnostic measures, which are estimated based on the training and testing CM data and adapts dynamically the trained parameters of the NHHSMM. The available CM data are acoustic emission data recorded throughout fatigue testing of open-hole carbon–epoxy specimens. RUL estimations from the ENHHSMM and NHHSMM are compared. The ENHHSMM is concluded as the preferable option since it provides more accurate outlier prognostics.Structural Integrity & Composite

Light scattering and rheological effects in an optical fibre coupled nanoparticle suspension

This study forms the first part of research into enhancing the forward and back scattering of light in an optical fibre using nanoparticles (NPs). This approach has the potential to enhance the sensitivity of optical fibre sensing by increasing the signal-to-noise ratio. The work described in this paper is focused on understanding the scattering of light by a suspension of NPs in refractive index matching liquid. It was noted early in the experimental work that rheological effects related to the viscosity and flow of the liquid affect the scattered light measured and therefore these effects are considered in the analysis. Gold nanoparticles in the tens to hundreds of micrometre size range were selected as the scattering particles based on their optical properties. These are suspended in a refractive index liquid with a similar refractive index to the optical fibre core. Effort was needed to transfer the NPs from their aqueous sodium citrate solution to the paraffin based solution. We investigated two types of interaction with the optical fibre: (i) dropping the NP suspension onto the end of a single-mode optical fibre and (ii) using the NP suspension as an interface between two single-mode optical fibres. It was noted that the surface tension of the liquid, the diameter of the fibre and the spacing between the fibres in case (ii) influence the reflected and transmitted light. In case of excess liquid, droplets flowed down the fibre and interestingly in case (ii) modified the reflected and forward transmitted light as it passed across the fibre interface. Our initial findings are that the influence of the gap between two optical fibres decreased after dropping refractive index liquid into the gap after fibre collimation, which is a beneficial result for understanding the influence of scattered light from a liquid containing NPs. Note, the position between the two fibres can also change due to the weight of the droplet and the fibre ends had to be re-collimated to investigate the influence of the moving droplets. These results will be expanded by additional experiments and modelling of the scattering from the nanoparticales and droplets.Structural Integrity & Composite

Effect of ultrasonic welding process on the crystallinity at the welding interface of CF/PPS joints

The influence of the ultrasonic welding process parameters, namely the force and the vibration amplitude, on the crystallinity degree at the welding interface of CF/PPS (carbon fibre reinforced poly(phenylene) sulphide) joints is investigated. Two different sets of parameters, one representing high force and high vibration amplitude (1000 N, 86.2 μm) and one representing low force and low vibration amplitude (300 N, 51.8 μm), were used in this study. The temperature at the centre of the overlap was measured using K-type thermocouples in order to obtain the cooling rate for each set of parameters. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) measurements were performed in order to determine the crystallinity degree of PPS at the welding interface. It was found that a force of 300 N and a vibration amplitude of 51.8 μm could obtain a PPS of a moderate crystallinity degree (14.6%) and an average PPS crystallite size of 41.3 Å, showing that it is possible to obtain a semi-crystalline welding interface by appropriately modifying the process parameters.Structural Integrity & CompositesAerospace Manufacturing Technologie